Stomach microbiome implicated in varying risk of stomach tumours

The stomach microbiome could play an important role in a person’s risk of tumour development, according to new research published in the journal PLoS Pathogens and funded by Worldwide Cancer Research.

Professor Mark Pritchard, senior author and study lead from the University of Liverpool, said: “Our study shows for the first time that there is a link between microbial diversity in the stomach and different health conditions that have similar pathologies. We believe this may partly explain why people with these different conditions have varying risk of stomach tumours.”

Most cases of gastric adenocarcinoma are associated with infection by the bacteria Helicobacter pylori (H. pylori), which causes loss of acid secreting cells in the stomach and a reduction in the level of stomach acid. However, other health conditions that cause a reduction in stomach acid, such as autoimmune gastric atrophy or chronic use of acid reflux medication (proton pump inhibitors, or PPIs), don’t have the same link to gastric adenocarcinoma. Autoimmune gastric atrophy is more frequently associated with a different type of stomach tumour called a neuroendocrine tumour and PPI use is not associated with an increased risk of stomach cancer.

This study reveals that people with H. pylori infection have a less diverse stomach microbiome than healthy people, that diversity of the microbiome was different between patients with autoimmune gastric atrophy and H. pylori induced gastric atrophy, and that chronic use of proton pump inhibitors had no effect on microbial diversity compared to healthy people. Although the development of gastric cancer is multifactorial, data from the present study suggest that the stomach microbiome may be a participating factor, according to the researchers.

The researchers were also able to identify metabolic process that were significantly more or less active as a result of the changing microbiome. The differences in the chemical products of these metabolic processes could help explain why an altered microbial diversity in the stomach affects the type of tumour a person may be at risk from based on their underlying health condition.

The researchers analysed the stomach microbiome of 95 people to test for difference in diversity caused by different health conditions. Using a technique called 16S rRNA sequencing they were able to determine the abundance of different bacterial species living in the study participant’s stomachs.

Dr Helen Rippon, Chief Executive of Worldwide Cancer Research, said: “The thousands of species of bacteria that live in us and on us are an essential part of our body’s ecosystem and we are just starting to understand how changes in them can influence our health, including the risk of developing cancer. We already know that one bug in particular, H.pylori¸ drives stomach cancer as well as causing ulcers, and this research tell us more about how other microbes might be involved too. Stomach cancer is one of the most common causes of cancer death worldwide and changing the make-up of stomach bacteria may one day help prevent or treat it. Worldwide Cancer Research is proud to have supported this key line of investigation.”